Unsymmetrically substituted piperazines



Patented Feb. 11, 1947 UNSYMMETRICALLY SUBSTITUTED PIPERAZIN ES Johannes S. Buck, East Greenbush, and Richard Baltzly, New York, N. Y., assignors to Burroughs Wellcome & Co. (U. S. A.) Inc., New

York, N. Y., a corporation of New York No Drawing. Application January 6, 1944, Serial No. 517,224

This invention relates to N-monosubstituted and N-N'-unsymmetrically disubstituted piperazines and has for an object to provide new compositions of the above type and a novel and improved method of making the same.

Another object is to provide a method of making and isolating the above substances which is suitable for commercial operation.

In our copending applicationSerial No. 476,914, file'd February 24, 1943, of which the present application is a continuation in part and in our copending application Serial No. 517,225, filed January 6, 1944, which is also a continuation in part, we have described certain methods for making and isolating substituted piperazines of the type CHz-CH:

where R is an aralkyl, or a higher alkyl, and R is either hydrogen or a second radical different from R.

The present invention refers to a new and different process for making any of the above compounds,'which new process can also be used for the production of numerous mono-N-substituted and unsymmetrically N,N'-disubstituted piperazines, many of which are not obtainable at all by any of the processes described in our above mentioned copending applications, nor by any of the methods known in the art.

The main difficulty involved in preparing monosubstituted piperazines, from which unsymmetrically disubstituted derivatives can also be obtained, resides in the isolation of the substance from the unreacted piperazine and the disubstituted piperazine' which are present and which in many cases have similar boiling points. Amines are extremely hard to separate by fractional distillation unless their boiling points are widely separated. Furthermore, the classical methods of separating secondary from tertiary amines are of no avail in this case, since a monosubstituted piperazine reacts as both a secondary and a tertiary amine. Even where a mixture containing monoand symmetrically disubstituted piperazines of widely different boiling points or solubilities is formed, the separation of the monosu'bstituted compounds from the disubstituted reaction products and the unreacted piperazine is frequently difiicult or even impossible if the stability of the introduced substituent is insufiicient to withstand the conventional separation methods such as fractional distillation.

9 Claims. (Cl. 260268) According to the-present invention, these difficultiespare overcome by treating piperazine with v fer in general to use palladium since, while equally or perhaps more eiiective invremoving a benzyl group, it is practically devoid of any tendency to reduce aromatic rings.

The term benzyl derivatives as used in the present specification and claims, includes the halogen derivatives such as p-chlorobenzyl and organic derivatives such as anisyl (CI-IzQCsHaCHa-J 4-phenyl-benzyl or alpha-menaphthyl (alpha naphthyl-methyl) The method according to the present invention permits the preparation of numerous monoalkyl, mono-acyl and other monosubstituted piperazines with a very high yield.

A particular advantages of the process according to the invention is that it is possible to obtain monosubstituted piperazines of the type CHrCHz CHz-CH: in which R is a radical, such as a lower alkyl having less than 8' carbon atoms, which when introduced into unreacted piperazine will not produce a separable mixture of monoe and di-' substituted compounds, or a radical such as an acyl; an aryl sulfonyl or a substituted aryl sulfonyl, which will produce such separable mixtures only under certain conditions, or a radical of relatively small inherent stability such as acyloxyalkyl, hydroxyphenalkyl, carbamido, substituted carbamido and carbamidino.

From the mono-N substituted piperazines obtained in this manner, unsymmetrically disubstituted piperazines of any desired type may be obtained by introducing on tothe first N nitrogen atom made available by the preceding catalytic hydrogenation, the desired substituent which is different from the substituent present in the monosubstituted compound but may be selected from the same group.

Thus, it is possible to produce unsymmetrically 'N-R, N'-R-disubstituted piperazines where R represents a radical selected from the group consisting of the lower alkyls having less than 8 carbon atoms, acyl, aryl sulfonyl, substituted aryl sulfonyl, acyloxyalkyl and hydroxyphenalkyl and R represents a radical selected from the group consisting of the lower alkyls having less than 8 carbon atoms, acyl, aryl sulfonyl, substituted aryl sulfonyl, acyloxyalkyl, phenacyl, substituted phenacyl, hydroxyphenalkyl; carbamido, substituted carbamido, thiocarbamido, substituted thiocarbamido and carbamidind.

The following examples may serve to illustrate, without limiting the invention.

Example 1 was dried over KzCOafland distilled in vacuo to separate pure monobenzyl piperazine from the dibenzyl piperazine.

The monobenzyl piperazine was methylated by the procedure of Clarke, Gillespie and Weisshauss (J. Amber. Chem. Soc., 55, 4571 (1933)), and the product, after liberation of the base was treated with benzoyl chloride to remove any monobenzyl piperazine that had remained unreacted. Basic material was again liberated with alkali and'distilled in vacuo. The product, N- benzyl-N'-methyl piperazine, was crystallized as the dihydrochloride from absolute alcohol-ether mixture and this dihydrochloride was hydrogenated catalyticallyin glacial acetic acid with the aid of palladized-charcoal. After filtration from the catalyst and evaporation of the solution in vacuo, the product, mono-N-methyl piperazine dihydrochloride was crystallized from methanolether.

Example 2 Piperazine hexahydrate was treated in absolute alcohol with p-chlorobenzyl chloride and the mono-N-p-chlorobenzyl piperazine was separated from the unreacted piperazine and from disubstituted piperazine by fractional distillation.

The mono-p-chloro-benzyl piperazine was rea Example 3 Mono-N-propyl piperazine. dihydrochloride was obtained in the process according to Example (equals alpha naphthyl-methyl) piperazine was separated as in Example 1.

Subsequently the monosubstituted compound was reacted with butyl chloride to yield N-alphanaphthyl-methylene-N'-butyl piperazine hydrochloride. On addition of 1 equivalent of hydrochloric acid and removal of the alpha-menaphthyl group by catalytic hydrogenation, mono-N- butyl piperazine dihydrochloride was crystallized from alcohol ether.

Example 5 Anisyl chloride (CHsO CsH4 CHzCl) (1 mol) (from anisyl alcohol (CmOC6H4CH2oH) and hydrogen chloride) was reacted with piperazine (1 mol) in absolute alcohol solution. The bulk of the dianisyl piperazine formed as a by-product separated towards the end of the reaction as its 'dihydrochloride and was filtered off. The solvent was evaporated from the filtrate, the residue diluted with water, basified and the anisyl piperazine extracted with ether.

The small amount of impurities remaining was separated by vac- 2, by using propyl chloride instead of ethyl bromide. V 1

Example 4 Piperazine hexahydrate was dissolved in absolute alcohol and an equimolecular amount of alpha-naphthyl methyl chloride was stirred into the solution. The mono-N-alphamenaphthyl uum distillation.

The mono-N-anisyl piperazine so produced was reacted in benzene with p-nitrobenzoyl chloride. The resulting compound, N-anisyl-N'-p-nitrobenzoyl piperazine hydrochloride separated and was recrystallized from alcohol. On drastic catalytic hydrogenation in alcoholic solution at room temperature with a platinum catalyst, first the nitro group was reduced to'an amino group and thereafter the anisyl group was split off to yield the mono-N'-p-amino-benzoyl piperazine dihydrochloride.

Example 6 Mono-N-p-chlorobenzyl piperazine as obtained according to Example 2, was treated with a slight excess of phenacyl bromide to yield N-pchloro-benzyl-N'-phenacyl piperazine. This was catalytically hydrogenated to mono-N'-(beta- "phenyl-beta-hydroxyethyl) piperazine.

Example 8 Anisyl chloride (CI-I30 Cal-I4 CHzCl (1 mol) (from anisyl alcohol (CHaOCeH4CH2OH) and hydrogen chloride) was'reacted with piperazine (1 mol) in absolute alcohol solution. The bulk of the dianisyl piperazine formed as a by-product separated towards the end of the reaction as its dihydrochloride and was filtered off. The sol-- vent was evaporated from the filtrate, the residue diluted with water, basified and the anisyl piperazine extracted with ether. The small amount of impurities remaining was separated by vacuum distillation.

The mono-anisyl piperazine so produced was treated with chloro-acetocatechol forming N- anisyl-N'-(3,4 dihyclroxyphenacyl) piperazine which was isolated as its dihydrochloride. Dras- Qt tic catalytic hydrogenation this compound at room temperature with a platinum catalyst yielded monoN-(beta 3, dihydroxyphenyl beta-hydroxyethyl) piperazine.

Example .9

N-benzyl piperazine as obtained according to Example 1, was dissolved in 95% alcohol and a slight excess of nitrourea was added. The solution was warmed cautiously until evolution of gas [had ceased. The solution was then acidified with HCl, evaporated and the product, N-benzyl- N'-carbamido piperazine hydrochloride purified by recrystallization from alcohol-ether mixture.

This product was catalytlcally hydrogenated in glacial acetic acid to yield mono-N' -carbamido piperazine.

Example The process according to Example 9 was repeated using phenyl isocyanate as a reagent instead of nitro urea. After catalytic hydrogenation mono-N'-phenylcarbamido piperazine was obtained.

Example 11 The process according to Example 9 was repeated using p-toluene-sulfonyl chloride as a reagent. The product obtained from subsequent catalytic hydrogenation was mono-N'-p-toluenesulfonyl piperazine monohydrochloride.

Example 12 The process according to Example 9 was repeated using p-acetamidobenzene-sulfonyl chloride as a reagent. Catalytic hydrogenation yielded mono-p-acetamidobenzene-sulfonyl piperazine monohydrochloride which was hydrolyzed by hydrochloric acid to ive mono-p-aminobenzene sulfonyl piperazine dihydrochloride.

Example 13 N-benzyl piperazine (Example 1) was warmed in dilute alcoholic solution with S-methyl isothiourea sulfate. Methyl mercaptan was evolved and from the solution, on evaporation and addition of acetone, N-benzyl-N'-carbamidino piperazine sulfate crystallized. It was purified by crystallization from aqueous acetone. Upon catalytic reduction, the benzyl group was eliminated and mono-N'-carbamidino piperazine sul-= fate was obtained.

Any of the mono-substituted compounds according to Examples 1 to may be treated with a suitable agent for introducing on to the free N a desired second substitutent. In this manner a great variety of unsymmetrically disubstituted piperazines can be produced. The following examples may serve as illustrations of said disub stituted compounds and of the methods of preparing the same. They are not intended to limit the scope of the invention.

Example 14 nated catalytically at room temperature with a platinum catalyst giving N-(beta-3,4-dihydroxyphenyl-beta-hydroxyethyl) N methyl piperazine.

Example 15 Example 16 Mono-N=ethyl piperazine as obtained from Example 2 was reacted with ethylene oxide to produce N-hydroxyethyi-N'-ethyl" piperazine. This was then benzoylated by the Schotten Baumanu method and the product derived by crystallization as the hydrochloride of N-benzoyloxyethyl-N'-ethyl piperazine.

Example 1 Mono-N-ethyl piperazine as obtained from Example 2 was treated with. chloro-acetocatechol to form N- (3,4-dihydroxyphenacyl) -N ethyl piperazine which was isolated. as its ciihydrc chloride.

Example 18 Mono -N-ethyl piperazine as obtained from Example 2 was reacted with p-toluene-sulfonyl chloride to yield N-p-to1uene-sulfonyl-N'-ethyl piperazine.

Example 19 Example 20 Mono-N'-propyl piperazine as obtained from Example 3 was reacted with p-acetamido-benzene-sulfonyl chloride to obtain N-p-acetamidobenzene-sulfonyl-N'-propyl piperazine.

Example al Mono-N'-butyl piperazine as obtained from Example 4 was treated with a slight excess of phenacyi bromide to yield N-phenacyi-N'-butyl piperazine.

Example 22 7.1 parts by weight of mcno-IV-bcnzoyloxyethyl piperazine dihydrochioride, a; obtained from Example 6, were dissolved in 50 parts of water and 2.8 parts of nitro urea and 4.2 parts of sodium bicarbonate were added with stirring and gentle warming. After standing at about G. for A; h the solution was evaporated in e residue extracted with 99% acetone. solution was filtered from undissolved solid their y sodium chloride) and acidified with hydrochloric acid. The product, N-carbamidol l'-benuoyloxyethyl piperazine hydrochloride, soon crystallized and was purified by recrystallization from aqueous acetone.

Example 23 Mono-N'-carbamido piperazine as obtained from Example 9 was treated with phenacyl bromide to yield N -phenacyl-N carbamido piperazine.

Example 24 Mon0 N'- (beta-phenyl beta-hydroxyethyl) pi perazine dihydrochloride, as obtained from Example '5, was treated with one equivalent of po- Example 25 Mono-N -benzoyloxyethyl piperazine dihydrochloride, as obtained from Example 6, was dissolved in ice water and the base liberated by careful addition of sodium hydroxidesolution. The oily base was extracted with benzene and the extract'was dried briefly over potassium car bonate. The solution was then treated with phenyl isothiocyanate to form N-phenylthiocarbamido-N-benzoyloxyethyl piperazine.

Other applications of our new method will readily occur to those, skilled in the art.

We claim:

1. In a method of preparing N-substltuted piperazines the steps of treating piperazine with an aralkyl halide having the general formula in which X is a halogen and Y is a radical of the group consisting of H and substituents unreactive in the reaction to form a reaction mixture, containing in additionto the unreacted piperazine and the symmetrically di-N-substituted piperazine, a substantial amount of mono-N- aralkyl substituted piperazine, separating the mono-N-aralkyl-substituted piperazine from the unreacted piperazine and from the di-substituted piperazine, introducingthe desired substituent on to the second (N') nitrogen atom of the mono- I aralkyl substituted piperazine, and then removing the aralkyl group by catalytic hydrogenation. 2. In a method of preparing N-substituted piperazines the steps of treating piperazine with an aralkyl halide having the general formula by catalytic hydrogenation.

3. Ina method of preparing N-monosubstituted piperazines the steps of treating piperazine with an aralkyl halide having the general formula in which X is a halogen and Y is a radical of the group consisting of H and substituents unreactive in the reaction to form a reaction mixture, containing in addition to the unreacted piperazine and the symmetrically di-N-substituted piperazine, a substantial amount of mono-N-aralkyl substituted piperazine, separating the mono-N- aralkyl-substituted piperazine from the unreacted piperazine and from the ell-substituted piperazine by fractional distillation, introducing on to the second (N') nitrogen atom of the monoaralkyl substituted piperazine a substituent selected from the group consisting of the lower alkyls having less than 8 carbon atoms, acyl, aryl sulfonyl, substituted aryl sulfonyl, acyloxyalkyl, hydroxyphenalkyl, carbamido, substituted carbamido and carbamidino, and then removing the aralkyl group by catalytic hydrogenation.

4. A method of preparing unsymmetrically -N-disubstituted piperazines comprising the steps in which X is a halogen and Y is a radical of the group consisting of H and substituents unreactive in the reaction to form a reaction mixture, containing in addition to the umeacted piperazine and the symmetrically di-N-substituted pipera zine, a substantial amount of mono-N-aralkyl substituted piperazine, separating the mono-N- aralkyl-substituted piperazine from the unreacted piperazine and from the disubstituted piperazine, introducing one of the desired substituents on to the second (N') nitrogen atom of the mono-N-aralkyl substituted piperazine, removing the aralkyl group by catalytic hydrogenation and introducing a second desired substituent diil'erent from said first substituent on to the first (N) nitrogen atom in place of the removed aralkyl.

5. A method of preparing unsymmetrically N- disubstituted pipers/zines comprising the steps of treating piperazine with an aralkyl halide having the general formula taining in addition to the unreacted piperazine and the symmetrically di-N-substituted piperazine, a substantial amountof mono-N-aralkyl substituted piperazine, separating the mono-N- aralkyl substituted piperazine from the unreacted piperazine and from the disubstituted piperazine, introducing on to the second (N') nitro gen atoms of the mono-N-aralkyl substituted piperazine a. substituent selected from the group consisting of the lower alkyls having less than 8 carbon atoms, acyl, aryl sulfonyl, substituted aryl sulfonyl, acyloxyalkyl and hydroxyphenalkyl, removing the aralkyl group by catalytic hydrogenation and introducing on to the first (N) nitrogen atom in place of the removed aralkyl a second desired substituent different from said first substituent, said second substituent being selected from the group consisting of the lower alkyls having less than 6 carbon atoms, acyl, aryl sulfonyl, substitutedaryl sulfonyl, acyoxyalkyl, phenacyl, substituted phenacyl, hydroxyphenacyl, carbamido, substituted carbamido, thiocarbamido, substituted thiocarbamido, and carbamidino.

6. A method of preparing N-carbamido-N'- benzoyl-oxyethyl piperazine comprising the teps of dissolving piperazine hexahydrate in absolute ethanol, adding benzyl cholride, distilling off the alcohol, extracting the reacted piperazine with ether, distilling in vacuo to separate mono-N- benzyl piperazine from dibenzyl piperazine, reacting the mono-N-benzyl piperazine with ethylene oxide to form N-benzyl-N'-hydroxyethyl pi- 'perazine, benzoylating toN-benzyl-N'-benzoyloxy ethyl piperazine dihydrochloride, hydrogenating with palladized charcoal in acetic acid to eliminate the benzyl group, treating the mono-N'- benzoyloxyethyl piperazine hydrochloride obtained in aqueous solution with nitro urea and sodium. bicarbonate, evaporating in vacuo and acidifying with hydrochloric-acid to form crystalline N-carbamido-N'-benzoy1oxyethy1 piperazine hydrochloride.

7. A method of preparing N-thiocarbamido-N- (beta-phenyl-beta-hydroxy ethyl) piperazine comprising the steps nf-dissolving'piperazine in absolute ethanol, adding benzyl chloride, distilling oiT the alcohol,.extracting'the reacted piperazine with ether, distilling in vacuo to separate mono- 'N-benzyl piperazine. from dibenzyl piperazine,

reacting the mono-N benzyl piperazine in alcohol solution with phenacylrbromide to form N- benzyl-N'-phenacy1 piperazine, acidifying this with hydrochloric :acid and hydrogenating it catalytically to remove the benzyl group and reduce the keto group so as'to yield mono-Nf-(betaphenyl-beta-hydroxyethyl) piperazine, treating this product in alcohol-solution with potassium thiocyanate and potassium bicarbonate in equivalent quantities and crystallizing the product, N- thiocarbamido-N'-(beta phenyl beta hydroxy ethyl) piperazine as its dihydrochloride.

8. N-carbamido-N'-benzoyloxyethyl piperazine. 9. An unsymmetrical N--RN.R' pipers,-

zine, where R is an acyloxyalkyl and R represents a radical selected from the group consisting of hydrogen, carbamido, substituted carbamido, thiocarbamido, substituted thiocarbamido and b n; JNHz JOHANNES S. BUCK. RICHARD BALTZLY.

REFERENCES CITED The following references are of record in the 1 file of this patent:

FOREIGN PATENTS Number Country Date OTHER REFERENCES French Feb. 3, 1931 

